diff options
Diffstat (limited to 'src/backend/utils/mmgr/aset.c')
| -rw-r--r-- | src/backend/utils/mmgr/aset.c | 25 |
1 files changed, 20 insertions, 5 deletions
diff --git a/src/backend/utils/mmgr/aset.c b/src/backend/utils/mmgr/aset.c index 7033042e2d8..0b017a40316 100644 --- a/src/backend/utils/mmgr/aset.c +++ b/src/backend/utils/mmgr/aset.c @@ -157,6 +157,14 @@ typedef struct AllocBlockData /* * AllocChunk * The prefix of each piece of memory in an AllocBlock + * + * Note: to meet the memory context APIs, the payload area of the chunk must + * be maxaligned, and the "aset" link must be immediately adjacent to the + * payload area (cf. GetMemoryChunkContext). We simplify matters for this + * module by requiring sizeof(AllocChunkData) to be maxaligned, and then + * we can ensure things work by adding any required alignment padding before + * the "aset" field. There is a static assertion below that the alignment + * is done correctly. */ typedef struct AllocChunkData { @@ -166,15 +174,19 @@ typedef struct AllocChunkData /* when debugging memory usage, also store actual requested size */ /* this is zero in a free chunk */ Size requested_size; -#if MAXIMUM_ALIGNOF > 4 && SIZEOF_VOID_P == 4 - Size padding; -#endif +#define ALLOCCHUNK_RAWSIZE (SIZEOF_SIZE_T * 2 + SIZEOF_VOID_P) +#else +#define ALLOCCHUNK_RAWSIZE (SIZEOF_SIZE_T + SIZEOF_VOID_P) #endif /* MEMORY_CONTEXT_CHECKING */ + /* ensure proper alignment by adding padding if needed */ +#if (ALLOCCHUNK_RAWSIZE % MAXIMUM_ALIGNOF) != 0 + char padding[MAXIMUM_ALIGNOF - ALLOCCHUNK_RAWSIZE % MAXIMUM_ALIGNOF]; +#endif + /* aset is the owning aset if allocated, or the freelist link if free */ void *aset; - /* there must not be any padding to reach a MAXALIGN boundary here! */ } AllocChunkData; @@ -327,8 +339,11 @@ AllocSetContextCreate(MemoryContext parent, { AllocSet set; + /* Assert we padded AllocChunkData properly */ + StaticAssertStmt(ALLOC_CHUNKHDRSZ == MAXALIGN(ALLOC_CHUNKHDRSZ), + "sizeof(AllocChunkData) is not maxaligned"); StaticAssertStmt(offsetof(AllocChunkData, aset) + sizeof(MemoryContext) == - MAXALIGN(sizeof(AllocChunkData)), + ALLOC_CHUNKHDRSZ, "padding calculation in AllocChunkData is wrong"); /* |